Magnetic materials



Patented Mar. 12, .1946

I David R. Howerton, Riverside, Ill'., assignor to Western Electric Company, Incorporated, New York, N. Y., a corporation of New York No Drawing.

Application November 5, 1942, Serial No. 464,661

' Y 6 Claims. (01. 15-10) This inventionrelates to magnetic materials and to a method of preparing the same,- and' more particularly to a method of preparing magnetic materials containing cobalt arid having low percentage carbon content.

In the manufacture of certain types of magnetic materials, such as Alnico, which contain aluminum, nickel, cobalt, copper and iron, an alloy may be prepared in general merely by heating the ingredients together. However, if any of the ingredients contain substantial percentages of carbon, special precautions must be taken to remove the carbon, the presence of carbon in amount aslittle as .10% being sufficient to seriously impair the residual induction and coercive forceof the magnetic material. Available refined cobalt contains relatively large amounts of carbon, the carbon content often being as great as l A An object of the present invention is to provide a method of preparing amagnetic material containing cobalt and having a low percentage carbon content.

I In accordance'with' one embodiment of the present invention, a master alloy containing all the cobalt required in the final alloy is prepared by combining cobalt, iron and nickel man are furnace. The alloy so obtained is. then compounded in an induction furnace with the proper amounts ofcopper and aluminum and such iron and nickel as may also be required to obtain the of a magnetic alloy of the type known as Alnico,

which comprises 7% to 9% aluminum, 13% to 15%nicke1, 22% to 26% cobalt, to 3.5% copper and the rest iron. a master alloy is prepared by placing a charge of cobalt, nickel and substantially pure iron in an arc furnace and covering the charge with anoxide slag suflicient to supply enough oxygen to oxidize the carbon tially all the cobalt required in the final alloy, the master alloy being prepared as described. a

present in the charge. Using, ,for example, .a

charge comprising approximately 81' pounds ot cobalt. 16 pounds of nickel and 53 pounds of and. the'cobalt containing approximately 1% carbon ore of the type known 'as hematite, or ferrous oxide, and 3 pounds of limestone should be added. The limestone melts and helps to make a fluid coveringfor the charge. The chargeis heated sufilciently high and for a suflicient period to cause the materials to completely alloy and to remove substantially all the carbon as carbon dioxide. In practice, it has been found that at 3100 F., in approximately fifteen minutes, the carbon content may be reduced to as little as .02% from a charge originally containing 31%.

The master alloy so obtained is then hot rolled intobillets or cast into pigs for convenience in charging the furnace in the next step. Inthis step, the required amount of cobalt, nickel and iron is charged into an induction furnace, all the cobaltthat is to be used in this step being supplied from the master alloy. An analysis of the master alloy ,is made and such additional nickel and iron as may be needed to obtain the desired proportions are added in the second step rather than in the preparation of the master alloy to facilitate control of the proportions of the final alloy. The carbon content of refined nickel and iron is low and, thus, these may be added latfi' to balance the proportions in the final alloy.

However. it is desirable to obtain as nearly as possible the desired proportions in the master extremely close control of the composition of'the melt, such losses as occur during the removal of the carbon in the master alloy being determined thereafter and the required additions made. By

using a master alloy charge to provide substancontaining cobalt and having approximately .02%

.carbon are consistently obtained.

In the second step, 126 pounds of the master alloy, prepared as described. 2 pounds of nickel and 13 pounds of iron are charged intoan induction furnace. The induction furnace produces a stirring action lathe melt which causes a thorough mixing. of the ingredients. These three metals are heated together until the temperature of the melt is between 2700 F. and 2900'F. and

, then5 pounds of copper may be added. However, the copper might be added in the master alloy if desired instead of in the final alloy. and the nickel may'also be added at either stage. The

addition oi the copper is deferred to this point in the process to enable the operator to reduce the temperature of the melt, as may be necessary to prepare it to receive the aluminum, it being somewhat simpler to increase the temperature of the melt by controlling the current in the furnace than to reduce it. After the copper has been added and the melt has reached the desired temperature, 13 pounds of aluminum may then be added and the melt poured into the desired form.

While but one embodiment of this invention has been described, it will be understood that this is merely illustrative and that the process disclosed may be applied to the preparation of many other alloys and may be modified in many respects without departing from the spirit or scope of the present invention.

What is claimed is:

1. A method of preparing a low carbon iron, cobalt, aluminum alloy which comprises melting iron and cobalt, oxidizing the melt to remove the carbon in said melt, casting the alloy, remelting the alloy, and adding aluminum to the melt.

2. A method of preparing a magnetic material of a low carbon iron cobalt aluminum alloy which comprises melting iron and cobalt under an oxidizing slag to remove the carbon present as an impurity in said ingredients, casting the alloy,

remelting the cast alloy, and adding aluminum to the melt.

3. A method of preparing a magnetic low carbon alloy of iron, cobalt, nickel, copper, and aluminum which comprises melting the cobalt and at least some of the ironbut no aluminum, oxidizing the melt to remove carbon present as an impurity in said melt, casting the melt, remelting the cast alloy, and adding the ingredients not added in the first melt.

4. A methodof preparing a low carbon magnetic alloy containing iron, cobalt and aluminum which comprises melting cobalt and iron in an arc furnace under an oxidizing slag, casting the alloy, remelting the alloy in an induction furnace, and adding aluminum to the melt.

5. A method of preparing a low carbon magnetic alloy containing iron, cobalt, nickel, copper and aluminum which comprises melting cobalt and some of the other ingredients but not aluminum in a furnace under an oxidizing slag, casting the melt, remelting the'cast metal and adding the remaining ingredients.

6. A method of preparing a low carbon magnetic alloy containing 7% to 9% aluminum, 13% to 15% nickel, 22% to 26% cobalt, 2.5% to 3.5% copper and the balance iron which comprises meltingall of the cobalt and some of the other ingredients including iron but not aluminum under an oxidizing slag, casting the melt, remelt- DAVID R. Ho'ron. 

